Bubble jet printer head with improved operational speed

Abstract

A bubble jet printer head comprises a base plate, an ink chamber provided on the phase plate, a device for supplying ink to the ink chamber, an ink passage provided on the base plate from the ink chamber to an orifice at a front end, and a heating element at the ink passage for heating the ink to form a bubble. The heating element includes a first electrode strip extending on the base plate to the ink chamber along the ink passage, an electrical insulator layer covering the first electrode strip except for the front and rear ends thereof, the electrical insulator layer having a front end facing the orifice, a resistance strip provided on the electrical insulator layer and having a front end in contact with the front end of the first electrode strip and extending rearwardly along and over the electrical insulator layer, and a second electrode strip provided on the electrical insulator layer in contact with the rear end of the resistance strip and extending rearwardly to the ink chamber along and over the electrical insulator layer.

What is claimed is: 
     
       1. A printer head of a bubble jet printer apparatus for ejecting a droplet of ink from an orifice by a dilational force of a bubble formed in the ink as a result of heating, comprising: a base plate comprising a substrate and a thermally insulating layer provided on the substrate so as to cover at least a part thereof in correspondence to where the ink is heated, said thermally insulating layer having a thickness which does not prevent quick dissipation of heat to the substrate;   an ink chamber provided on the base plate for accepting the ink;   means for supplying the ink to the ink chamber;   an ink passage provided on said base plate in communication with the ink chamber at a first end thereof and to the orifice at a second end thereof for passing the ink from the ink chamber to the orifice; and   heating means provided on the thermally insulating layer in correspondence to said ink passage for heating the ink therein to form said bubble, said heating means comprising: a first electrode strip provided on the thermally insulating layer so as to extend to the ink chamber along the ink passage,   an electrical insulator layer provided so as to cover the first electrode strip except for a first end thereof away from the ink chamber and a second end thereof close to the ink chamber, said electrical insulator layer having a front end facing the orifice such that the first end of the first electrode strip is exposed at the front end of the electrical insulator layer,   a resistance strip provided on the electrical insulator layer with a first end thereof in contact with said first end of the first electrode strip and extending along the electrical insulator layer toward the ink chamber, covering the front end of the electrical insulator layer, such that the resistance strip acts as a heat source generating heat in response to an electric current flowing therethrough between the first end and the rear end thereof,   a second electrode strip provided on the electrical insulator layer in contact with a second end of the resistance strip and extending to the ink chamber along the electrical insulator layer,   a heater protective film provided on the resistance strip for protecting the resistance strip from corrosion, and   an electrode protective film provided on the second electrode strip for protecting the second electrode strip from corrosion;     wherein said substrate has a thermal conductivity which is at least twenty times greater than that of the thermally insulating layer.   
     
     
       2. A printer head as claimed in claim 1 in which the thermal conductivity of said substrate is at least seventy times larger than that of the thermally insulating layer. 
     
     
       3. A printer head as claimed in claim 1 in which the thermal conductivity of said substrate is at least seventy-seven times greater than that of the thermally insulating layer. 
     
     
       4. A printer head as claimed in claim 1 in which said substrate comprises silicon and said thermally insulating layer comprises silica. 
     
     
       5. A printer head as claimed in claim 1 in which said substrate comprises alumina and said thermally insulating layer comprises silica. 
     
     
       6. A printer head as claimed in claim 1 in which said heater protective film comprises a carbon film having structure in which atomic arrangement is similar to that of diamond. 
     
     
       7. A printer head as claimed in claim 6 in which said heater protective film has a thickness in a range from 0.01 μm to 10 μm. 
     
     
       8. A printer head as claimed in claim 7 in which the thickness of the heater protective film is between 0.05 μm and 5 μm. 
     
     
       9. An ink jet printer head as claimed in claim 8 in which the thickness of the heater protective film is between from 0.05 μm and 3 μm. 
     
     
       10. A bubble jet printer head comprising: a base plate having a top surface and a front end and a rear end;   a cover plate coupled to the base plate and facing said top surface of the base plate to define between the two plates an ink chamber at the rear end of the base plate and a number of ink passages running from the ink chamber toward the front end of the base plate and terminating in respective ink ejection orifices;   said base plate comprising a substrate having a top surface and a thermally insulating layer covering at least selected portions of said top surface of the substrate;   heating means provided on the thermally insulating layer and aligned with said ink passage for heating the ink therein to form bubbles, said heating means comprising for each of said ink passages: a first electrode strip provided on the thermally insulating layer and extending from the ink chamber end of the ink passage toward the orifice of the ink passage;   an electrical insulator layer covering the first electrode strip except for a front end thereof and a rear end thereof to thereby leave uncovered by said first electrical insulator layer a front end of the first electrode strip facing the orifice and a rear end of said first electrode strip facing the ink chamber;   a resistance strip provided on the electrical insulator layer to serve as a heat source and having a front end which is in contact with and covers said front end of the first electrode strip and extending rearwardly over and along the electrical insulator layer toward the ink chamber and having a rear end facing the ink chamber, said resistance strip acting as a heat source generating heat in response to an electric current flowing therethrough between the front end and the rear end thereof;   a second electrode strip provided on the electrical insulator layer in contact with the rear end of the resistance strip and extending rearwardly over and along the electrical insulator layer toward the ink chamber;   a heater protective film provided on the resistance strip to protect said resistance strip; and   an electrode protective film provided on the second electrode strip to protect said second electrode strip;     wherein the thermal conductivities and thicknesses of said substrate and said thermally insulating layer are selected to cause rapid initial build up of heat at the resistance strip when the resistance strip is first energized by the passage of current therethrough and thereafter to cause rapid dissipation of heat from the resistance strip through the thermally insulating layer into the substrate.   
     
     
       11. A bubble jet printer head as in claim 10 in which the thickness of said thermally insulating layer is about 1 micron or less and the thickness of the substrate is many microns and the thermal conductivity of the substrate is at least 20 times that of the thermally insulating layer.